Electrolytic precipitation of uranium from the ion exchange eluates



Ap 5 R. KUNIN ELECTROLYTIC PRECIPITATION OF URANIUM FROM THE ION EXCHANGE ELUATES Filed April 7, 1954 Permselecfive Membrane INVENTOR. ROBERT KUNIN BY ffi United States Patent 1O "ice 2,832,727 I ELECTROLYTIC PRECIPITATION F FROM THE ION EXCHANGE ELUATES 7 Robert Kunin, Trenton, N. 1., assignor, by me sne assignments, to the United States of America as represented by the United States Atomic Energy Commission Application April 7, 1954, Serial No. 421,667 11 Claims. (Cl. 204-15) This invention relates to the recovery of uranium. It relates to an electrolytic process wherein uranium oxide and/ or hydroxide is precipitated and is isolated from aqueous solutions which contain soluble uranium salts.

In the leaching of uranium-bearing ores the uranium is extracted as a complex anion of an acid. In a subsequent step, the solution of the complex acid is passed through a column or bed of particles of an ion exchange resin, preferably a strongly basic, quarternary ammonium, anion exchange resin. The uranium complex is adsorbed by the anion exchangeresin and is removed from the leach liquor. Next, an aqueous solution of a mineral acid and an alkali metal or ammonium salt 01: the mineral acid, such as a solution of, nitric acid and sodium nitrate, is passed through the mass of resin. The uranium is thereby removed; 1' e., eluted, in the form of a dissolved uranyl salt having the formula UO;,(X) in which X is one equivalent weight of an acid radical such as a nitrate radical, --N0 sulfate radical, -SO or a chloride radical, Cl. Thissolution of uranyl salt which also contains some of the acid and salt is called the eluate.

The object of this invention is to treat such an eluate so as to convert the uranyl salt into the form of an insoluble hydrated oxide which can be readily isolated and ignited to the oxide, U 0

This object is accomplished efliciently and economically by a method of electrolysis wherein a direct electric current is passed through an electrolytic cell which is divided by means of a permselective membrane intoa cathode compartment containing the above-mentioned eluate and an anode compartment containing a solution of an alkali metal salt or an ammounium salt-preferably a sodium salt-of the acid which was used for elution. Preferably the anolyte is a solution of sodium nitrate or sodium chloride.

The electrolytic cell which is employed can best be understood by a reference to the attached drawing wherein the single figure is a diagrammatical representation of a typical cell which is divided into an anode compartment'and a cathode compartment by means of a permselective membrane or diaphragm. In said figure, 1 rep-.

resents a container which is divided into two compartments, 5 and 6, by a permselective membrane, 2, which is described in greater detail below. CompartmentS is an anode compartment by virtue of the presence there of the anode 3, while compartment 6 is a cathole com partment because it contains the cathode 4. When the cell is in operation, the electrodes are connected to a source of electric power not shown.

, .The cell which is employed in this invention can be varied as to size, shape, vents, ports, exits, construction materials, controls, embellishments, et cetera without departing from the spirit of this invention. What is essential is that the cell have two compartments, one containing the anode and the othercontaining the cathode, and that vthe two compartments be separated by a permselective membrane as defined herein.

, 2,832,727 Patt rned Apr. 29,; 195's:

The permselective membranes which divide the elec trolysiscell into the two compartments areall important to the success of this process. They function by allow ing only ions of one sign-either anions or cationsto pass through them while at the same time preventing the passage of ions of the opposite sign from one compartment to the other. Cationic permselective membranes are those which allow the passage of cations while anionic permselective membranes are those which permit the passage of anions. The membranes contain ion exchange resins and it is the presence of the ion exchange resins which imparts the property of permselectivity. While the composition of the permselective membranes can vary within reasonable limits, it is important that they contain enough ion exchange resin as to have suitably high conductance'when employed in the electrolysis cell. The permselective films which have proven to be most suitable for use in this process are those made by incorporating particles'of anion exchange resin in a filmforming matrix such as polyethylene or vinyl resins.

Such membranesare available commercially.

.which, because it is anionic, allows the passage of. only anions.

When a cationic permselective membrane is employed,

In the process of this invention, an eluate which is an' aqueous solution of a uranyl salt together with a mineral acid and an alkali metal salt or an ammonium salt of the mineral acid is placed in the cathode compartment of the electrolysis .cell. The anolyte which is employed is ordinarily As electrolysis proceeds, hydrogen is liberated at the cathode, the catholyte decreases in acidity, and the UO ion is'reduced to U++++. The uranium commences to precipitate as an oxide and continues to do so as the pH of the catholytegradually approaches neutral. As neutrality is reached, the precipitation is essentially complete, and the electrolysis could be terminated. It has been noticed that if the electrolysis is continued for just a few seconds the pH of the catholyte will rise almost perpendicularly, if charted graphically, from the neutral point to as high as analytical orprocess control tool. However, it should be noted that electrolysis is carried out, for all intents and purposes, with an acidic catholyte.

The precipitate is readily removed from the catholyte by conventional means such as filtration or centrifuging When nitrate or sulfate ions are involved, there is a liberation of oxygen. In any case, however, the anolyte becomes increasingly acidic and ultimately reaches the point where it contains both salt and acid. At this point it is entirely suitable for eluting more adsorbed uranium complex from another bed of exhausted anion-exchange resin. During electrolysis, cations in the 'anolyte migrate toward the cathode but are constrained from entering the cathode compartment by the anionic membrane alkali metal ions in the anolytemigrate through the membrane into the catholyte and the current is carried by them. In such a case, however, the ultimate resultis the same as when an anionic membrane is used, Uranium is precipitated in the cathode compartment and the anolyte becomes acidic so that it can be used for elution.

Furthermore, after removalof the uranium, the catholyte contains alkali metal salts and it can be, and should be, used as the anolyte in the electrolysis of subsequent batches of eluate.

a solution of the same alkali metal salt or ammonium salt as is present in the eluate.

12. This fact makes it very'simple to determine the end of the electrolysis and is a handy Actually, the' electrolytic process described above can ing resins in a cyclic or continuous process. For example, an eluate is run into" the cathode compartment of an alkali metal salt ot a mineral acid from the class consisting of hydrochloric acid, nitric acid and sulfuric acid,-

.said cathode and anode compartments being separated-by 'salt of'sa'id mineral acid, and an anode ccimpartmentha'vthe electrolytic "cell described above through which is 5 a permselective membrane which contains an ionexpassing a direct current As the uranium-precipitates, change resin, continuing the passage of current until: the

a the catholyte is removed and filteredand the filtrate is] hydrated uranium oxidehas precipitated and thereafter 7 passed into the anode compartment. At the same time separating saidprecipitated uranium compound from said the anolyte which has 'becomeacidic is withdrawn and catholytej T i is used for eluting a bedof anion exchange resin which 10 2. The process of claim 1 in which the permselective contains adsorbed uranium complex. V membrane contains an anion exchange resin. Y

It is, therefore, apparent that by means of this elec- 3. The process ofclaim 1 in which the permselective troly-tic process uranium'is obtained very efiiciently. And, membrane" contains a cation exchange resin. furthermore, only electrical power is -consumed. "There 7 4. The process of claim 1 additionally including the I is no need for shipping, storing, and-discarding chemicals. .15 step of igniting the hydrated uranium oxide to U les a A process for the isolation of iiranium compounds,

- 1p V which comprises passing a direct electriccurrent through Vari ushu s 10 1 ai ing ranyl sa tm i acids, an electrolytic cell comprising a cathode compartment n 'm l or mm n m salts of the ei r p y having therein an acidic aqueous solution Which is made as catholytes in the electrolytic process described above. up of iranyl nitrate, an alkalimetal nitrate and nitric, Aqueous'sollltions of the corresponding metal or ammo: 7 id, d) a anode 'cornpartment'having I therein an nium salts were employed "as anolytes. The cells were acidic aqueous solutiml W-llich is made'l p of an alkali constructed of polymethylmetha'crylate (Plexiglas). .The t l it t aid th d d a d eqmjpgrtmems be- V electrodes were platinum, although carbon and copper 7 j arated by apermselective membrane which 6,0 1

are quite satisfactory as cathodes; .With nitrate anolytes tains an ion exchangeresin, continuing the passa'geiof' graphite anodes show reasonable durability whereas lead cgrrentuntil the oxide hydrated uranium has precipitated,

. anodes are satisfactory with sulfate 'anolytes and can ref nd ther after separating said precipitated uranium 10am: place the platinum. The cells were divided into anode n df id gatholyfg and cathode compartments by meansof eitheran anionic 6; The process of claim 5 in which the permselectiye or .a cationic permselective membranefAmberplex A1 m b t i anamongemhange rgsjnp V or C1) known'to contain about 70% ion exchange resin 7. The processof claim 5 .in .Which the permsclec ivfi in a matrix of polyethylene and known :to have been embrane Icontainsa jcation exchange resin; 7 7 made according to the p o s of 8. Pa pp I 8. The process of claim 5 additionally including the tions Serial Nos. 202,577 and 205,413,.now U. S; Patents step of igniting thehyd-rated uranium pxideto U 03- Nos. 2,681,320 and 2,681,319 respectively, and the cor: r 9 Acyclic process .for isolating anranium compound responding Canadian Patents :Nos. 493,562 and v493,563 which. is adsorbed on a bed ,of particles of an anionexof June 9, 1953, The cationic membranes contained a changeresin which comprises first eluting said adsorbed cation .exchangere'sin' which was-asulfonated.eross=linked q compound by passing aqueous solution of a mineral copolymer of styrene anddivinylbenzene while .the an.- i acid from the class consisting of hydrochloric acid, nitric ionic membranes contained an anion exchange resin made 40 acid 'and'sulfuric acid and an alkali metal salt of the by. aminating With a tertiary amine a cross-linked, .ChldIO mineral acid th -Qugh' said bed of resin, collecting the methylated copolymer of styrene and divinylben'zene. eluate;which .containsI-he uraniumin the form of a many! "During electrolysis the .anolytes'and catholytes were salt of said acid; electrolyzing'said eluate inthe cathode mechanically agitated. The direct current was passed compartment of an electrolytic cell .whichjcontains a until the formation .of a precipitate appeared to the com.- cathode compartment and an anode compartment sepplete, after which the catholyte :was filtered to remove-the arated by a permselective membrane containing an Zion jhy-drated uranium oxide. The filtrate and the .anolyte exchange, resin, said anode compartment coptaining an 'wereanalyzed. 7 aqueous solution of an alkali metal salt of the mineral I the results which are tabulated below the concenl- I acid present :in said eluate; conti-nuing ;.thie electrolysis 'tration of the acids and salts is expressed in normality nntil'an insoluble uranium compound has precipitated;

' .(N), A. E., percent, represents the percent of ampere removing said uranium precipitate and transierring-the efiicicncytof the process, and the concentration .of uranir' remaining solution to the anode compartment of an elec; um (2U isex'prcssed in grams per liter 1(gl/ l.'-). Anionic trolysis ,cell which is divided into an anode compartperm-selective membranes were employed in obtaining the ment and a cathode compartment 'by means of ,a permdata helowgbut essentially the .same results tareobtained 'selective membrane containing an ion exchange resin; 1 through theuselof acationic membrane. c removing the anolyte from said firstlelectrolytic cell and r 1 Cathode Solution Anode Solution InitialSalt 'InltialAcld I Initial Final Final Initial Salt Final A. E.,

' a T "PH" W's-l 1 Ac Pe cent t 11.4 0.04 0.9N KNOa. 0.19N 5 7.5 0.03 10.9N KNOsL..' 0.19: 89 5' 6.7 0. 0 :0.9N NH4OI..- 0. .20 flea-;, .5 0.00; '1.8N M12504-.- 0.56 ,00- 15 4.8 0.00 0.9N NaNQ n 9.2;; .83

:,I l aimi f V V transferring it to a bed of particles of an anion exchange 1.;Alprocess for theisolation of uranium compounds, resin on which ;isj.adsorbed a u aiuni ompound;*end whichcbmprises passing' a'directelectric current through repeating the-electrolysis operation ano nt. distribution a electrolytic cellcomprising a-cathode compartment 70 pfth jprgqdnctg'l f h eleq fiilyfic 'ha ingther-ein-an acidicaquebus'solution which ismadc ll 0. The process of cl i 1 v V up;of"(d) a mineral acid from the class consisting of-hy lution p iner al ga oit l and allgali v p droch'lorio acidynitric acjidand sulfuric acid and (b) all nitric a d and sodillniinitrat e.

alkali metal salt of said mineralaci-dand (c) a uranyl 1 1. Aproc'ess for: (a) recovering uranium in' the form 76 of uranium oxide and hydroxide lfrom anaqueeus sollition derived from the elution of uranium complexes adsorbed by ion-exchange resins, and '(b) for simultaneously reconditioning the eluate for further use in such elutions, said process comprising placing in the cathode compartment of an electrolytic cell, formed from a suitable container having a cathode and an anode compartment separated from each other by an ion-exchange resin-impregnated permselective membrane, an aqueous solution of a mineral acid from the class consisting of nitric, hydrochloric and sulfuric acids together with an alkali metal salt of said mineral acid and a uranyl salt of said mineral acid, placing in the anode compartment of said cell an aqueous solution of an alkali metal salt of a mineral acid, passing direct current through said cell until an insoluble uranium compound has precipitated in the catholyte, and filtering off the uranium precipitate from the catholyte, whereby the filtrate ismade usable as the anolyte in a repetition of said process on another sample of eluate and after serving as the anolyte may be used in eluting a bed of ion-exchange resins which contain adsorbed uranium complexes.

1,448,036 Pearson et a1 Mar. '13, 1923 2,581,863 Kahn Jan. 8, 1952 2,733,200 Kunin Jan. 31, 1956 2,733,202 Boyer Jan. 31, 1956 2,739,934 Kunin Mar. 27, 1956 2,743,222 Clevenger Apr. 24, 1956 2,776,184 Kamen Jan. 1, 1957 2,781,303 Boyer et al. Feb. 12, 1957 FOREIGN PATENTS 626,882 Great Britain July 22, 1949 493,562 Canada June 9, 1953 7 493,563 Canada June 9, 1953 704,602 Great Britain Feb. 24, 1954 OTHER REFERENCES Analytical chemistry of the Manhattan Project, C. J. Rodden, 1st ed., McGraw-Hill Book Co., New York, 1950; Div. VIII, pages 523-525.. 

1. A PROCESS FOR THE ISOLATION OF URANIUM COMPOUNDS, WHICH COMPRISES PASSING A DIRECT ELECTRI CURRENT THROUGH AN ELECTROLYTE CELL COMPRISING A CATHODE COMPARTMENT HAVING THEREIN AN ACIDIC AQUEOUS SOLUTION WHICH IS MADE UP OF (A) A MINERAL ACIF FROM THE CLASS CONSISTING OF HYDROCHLORIC ACID, NITRIC ACID AND SULFURIC ACID AND (B) AN ALKALI METAL SALT OF SAID MINERAL ACID AND (C) A URANYL SALT OF SAID MINERAL ACID, AND AN ANODE COMPARTMENT HAVING THEREIN AN ACIDIC AQUEOUS SOLUTION WHICH IS MADE UP OF AN ALKALI METAL SALT OF A MINERAL ACID FROM THE CLASS CONSISTING OF HYDROCHLORIC ACID, NITRIC ACID AND SULFURIC ACID, SAID CATHODE AND ANODE COMPARTMENTS BEING SEPERATED BY A PERMESELECTIVE MEMBRANE WHICH CONTAINS AN ION EXCHANGE RESIN, CONTINUING THE PASSAGE OF CURRENT UNTIL THE HYDRATED URANIUM OXIDE HAS PRECIPITATED AND THEREAFTER SEPARATING SAID PRECIPITATED URANIUM COMPOUND FROM SAID CATHOLYTE. 